AM3874 datasheet(260/361 Pages) TI

260 / 361 page

AM3874, AM3871

SPRS695C – SEPTEMBER 2011 – REVISED DECEMBER 2013

www.ti.com

Table 8-40. TMDS Routing Specifications (continued)

PARAMETER

MIN

TYP

MAX

UNIT

TMDS differential pair to any other trace spacing

2*DS(2)

(2)

DS = differential spacing of the HDMI traces.

8.9.1.3

DDC Signals

As shown in Figure 8-37, HDMI Interface High-Level Schematic, the DDC connects just like a standard

I2C bus. As such, resistor pullups must be used to pull up the open drain buffer signals unless they are

integrated into the ESD protection chip used. If used, these pullup resistors should be connected to a 3.3-

V supply.

8.9.1.4

HDMI ESD Protection Device (Required)

Interfaces that connect to a cable such as HDMI generally require more ESD protection than can be built

into the outputs of the processor. Therefore, this HDMI interface requires the use of an ESD protection

chip to provide adequate ESD protection and to translate I2C voltage levels from the 3.3 V supplied by the

device to the 5 volts required by the HDMI specification.

When selecting an ESD protection chip, choose the lowest capacitance ESD protection available to

minimize signal degradation. In no case should the ESD protection circuit capacitance be more than 5 pF.

TI manufactures devices that provide ESD protection for HDMI signals such as the TPD12S521. For more

information see the www.ti.com website.

8.9.1.5

PCB Stackup Specifications

Table 8-41 shows the stackup and feature sizes required for HDMI.

Table 8-41. HDMI PCB Stackup Specifications

PARAMETER

MIN

TYP

MAX

UNIT

PCB routing/plane layers

Layers

Signal routing layers

Layers

Number of ground plane cuts allowed within HDMI routing region

Cuts

Number of layers between HDMI routing region and reference ground plane

Layers

PCB trace width

Mils

PCB BGA escape via pad size

Mils

PCB BGA escape via hole size

Mils

MPU device BGA pad size(1)(2)

0.4

(1)

Non-solder mask defined pad.

(2)

Per IPC-7351A BGA pad size guideline.

8.9.1.6

Grounding

Each TMDS channel has its own shield pin which should be grounded to provide a return current path for

the TMDS signal.

260

Peripheral Information and Timings

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